Yes, Frodo actually did a brief narration towards the end of ROTK, perhaps PJ will have him do some TH narration as well.

It's good to finally have some casting information,even non fully official.The Deadline article also suggests that 'Returning actors will need to be locked in shortly',so there won't be long before we have the announcements.

All that is gold does not glitter, Not all those who wander are lost; The old that is strong does not wither, Deep roots are not reached by the frost.